The field of the invention is methods of applying flexible coatings to substrates, the improved coating compositions used, and the coated articles resulting therefrom. More particularly, the invention is concerned with the curing of thermosetting epsilon-caprolactone modified acrylic polymers and aminoplast cross-linking agents based coating compositions on flexible as well as rigid substrates such as automotive vehicle exteriors.
Changes in the automotive industry have resulted in the use of many new materials in the manufacturing of automobile parts. The properties of these materials place new demands on the coating compositions used to protect them and make them aesthetically appealing. Automobiles of the 1980's have some flexible plastic parts in the areas of the front and rear bumpers to prevent damage from minor bumps. These parts require paints that are extremely flexible over a wide range of temperatures, durable to weathering, and aesthetically pleasing. The prior art coating compositions for these flexible parts are based upon high molecular weight polyester-urethane polymers cured with aminoplast resins. These thermoset polyester-urethanes exhibit excellent initial flexibility, but the flexibility deteriorates rapidly when the coated article is exposed to even normal weathering. Because the most suitable polyester-urethanes are very high in molecular weight, these polymers are unsuitable for high solids, solvent-borne coatings.
The state of the art of these polyester-urethane polymers is illustrated by the DURETHANE.RTM. coating compositions of PPG as illustrated in their Information Bulletins for DEL-32 906, and DEM-32 797, the disclosures of which are incorporated herein.
The state of the art of epsilon-caprolactone modified acrylic polymers and aminoplast cross-linking agent based coating compositions may be ascertained by reference to U.S. Pat. No. 4,082,816, of Fisk et al, the article by B. E. Bailey et al entitled "Caprolactone in Surface Coatings", as reported in the Journal of the Oil Colour Chemistry Association (1981), Volume 64, at pages 398-404, the article by A. Schindler et al entitled "Alcohol-Initiated Polymerization of Epsilon-Caprolactone" in the Journal of Polymer Science: Polymer Chemistry Edition, Volume 20 (1982) at pages 319-326, and the article by A. N. Theodore et al entitled "Modification of Acrylic Polymers etc." in the Journal of Coatings Technology, Volume 54, No. 693, 10/82, pages 77-81, the disclosures of which are incorporated herein.
Acrylic microgel resins are useful in the present invention and the state of this technology may be ascertained by reference to U.S. Pat. Nos. 4,220,679; 4,290,932, and 4,340,511, the disclosures of which are incorporated herein.